About the self-cleaning potential of TiO2-TEOS treatments for heritage cementitious materials

20th century architectural heritage has been exposed to increasingly aggressive environmental conditions, including pollutants and particulate matter in the atmosphere, which cause soiling on the surface and progressive deterioration. Hence, conservation has become a priority for this heritage, especially focusing on cement-based materials and concrete. In this paper, two self-cleaning TiO2-based treatments were applied to different types of cement mortar slabs, representative of 20th century architecture. The first treatment consists of a TiO2 nano-particles dispersion in ethyl silicate, applied by brushing; in the second treatment, ethyl silicate was applied first and then cellulose pulp with a dispersion of TiO2 was added. Treatments were first applied to smooth mortar slabs with aggregates of different chemical compositions. Then, the texture's effect was considered, and the treatments were applied to mortars slabs with different surface finishing mimicking the ones used in 20th century architecture. Standard laboratory tests were carried out, together with a new customized procedure designed to simulate real-world conditions, with artificial soiling and rain cycles, to evaluate the treatments' cleaning efficacy. The results allowed to assess the efficacy of the treatments and to find differences in their photocatalytic activity, regarding both superhydrophilicity and photodegradation effects, on different substrates. Moreover, the results highlight the limits of some standard testing procedures, which may not be suitable for heterogeneous substrates and irregular surfaces, and the need for new protocols.